Revert "device: use wgcfg key types"

More cleanup work of wgcfg to do before bringing this in.

This reverts commit 83ca9b47b6.

device/noise-helpers.go

@@ -7,10 +7,12 @@ package device
 
 import (
 	"crypto/hmac"
+	"crypto/rand"
 	"crypto/subtle"
 	"hash"
 
 	"golang.org/x/crypto/blake2s"
+	"golang.org/x/crypto/curve25519"
 )
 
 /* KDF related functions.
@@ -73,3 +75,28 @@ func setZero(arr []byte) {
 		arr[i] = 0
 	}
 }
+
+func (sk *NoisePrivateKey) clamp() {
+	sk[0] &= 248
+	sk[31] = (sk[31] & 127) | 64
+}
+
+func newPrivateKey() (sk NoisePrivateKey, err error) {
+	_, err = rand.Read(sk[:])
+	sk.clamp()
+	return
+}
+
+func (sk *NoisePrivateKey) publicKey() (pk NoisePublicKey) {
+	apk := (*[NoisePublicKeySize]byte)(&pk)
+	ask := (*[NoisePrivateKeySize]byte)(sk)
+	curve25519.ScalarBaseMult(apk, ask)
+	return
+}
+
+func (sk *NoisePrivateKey) sharedSecret(pk NoisePublicKey) (ss [NoisePublicKeySize]byte) {
+	apk := (*[NoisePublicKeySize]byte)(&pk)
+	ask := (*[NoisePrivateKeySize]byte)(sk)
+	curve25519.ScalarMult(&ss, ask, apk)
+	return ss
+}